1. Field of the Invention
The present invention relates generally to semiconductor device fabrication methods and semiconductor devices, and more specifically to methods of fabricating semiconductor devices having a trench isolation structure isolating elements of the semiconductor device, and semiconductor devices.
2. Description of the Background Art
A shallow trench isolation (STI) structure is generally used as a structure isolating elements of a semiconductor device. In this STI structure a trench is formed in a main surface of a semiconductor substrate and it then internally has oxide film buried therein to provide electrical insulation between adjacent elements.
When this STI structure is applied to a conventional semiconductor device it has a trench having a geometry closer to a rectangle and having a sidewall and a bottom surface together forming a substantially right angle, since in recent years semiconductor devices are required to be microfabricated an element isolation is accordingly required to be more microfabricated. As such the trench would have a steep sidewall and in an interconnection process when a contact is made with an active region adjacent to the trench a mask can be misregistered or the contact may have a variation in diameter and a trench isolation film can be removed. Furthermore, if the trench isolation film can be removed significantly; the contact can reach a semiconductor substrate region underlying the isolation film and thus have a significant effect on electrical characteristics.
Furthermore the STI structure often has a trench with an internal wall nitrided or provided with nitride film to prevent a junction from having significant defective leakage of electricity resulting from stress concentration introduced at a corner formed by the trench's sidewall and bottom surface that is attributed to a thermal history in a process for fabricating a semiconductor device. To prevent this, the trench has an internal wall nitrided or provided with nitride: film to alleviate stress.
If a trench has an internal wall nitrided or provided with nitride film to prevent a junction from having significant defective leakage of electricity, however, an oxide film close to a portion serving as a gate oxide film would also be nitrided or after a gate oxide film is formed a nitride film would exist closer thereto and as a result an electron is trapped and electrical characteristics are thus impaired. This is significantly observed particularly when the STI structure is applied to a non-volatile semiconductor device, and it may result in a reduced yield and have a significantly negative effect on the reliability of the product. Thus there is a demand for a trench isolation structure capable of preventing a junction from having defective leakage of electricity, and also capable of ensuring a reliable gate oxide film.